Modular fiber optic cable splitter

ABSTRACT

An optical interface includes a rack mountable enclosure that includes multiple slots for retaining multiple insertable fiber optic (FO) modules. The FO modules include a first set of interconnection ports that connect to remote radio units (RRUs), a second set of interconnection ports that connect to a baseband unit (BBU), and a third set of monitoring ports that connect to monitoring/text equipment. The FO modules contain fiber splitters that split off uplink/receive and downlink/transmit signals carried on optical fibers to the third set of monitoring ports. The FO modules may insert in different orientations and directions into different rack mountable enclosure configurations for higher density and more configurable connectivity. A splitter holder is located within the FO module and provides improved optical fiber routing for more integrated module port interconnectivity.

BACKGROUND

Until recently, most wireless communications sites included radiosystems located on the ground level in a building, cabinet or othershelter. The direct current (DC) power supply, baseband controller,amplifiers and radios were historically located in one location withinthe shelter. From this location, coaxial cable was run from the radiosto antennas that were supported on a tower outside the building.

Latest generation wireless communications systems, referred to asdistributed antenna systems (DAS), distributed DC radio systems, remoteradio heads (RRH), 4G and long term evolution (LTE) cellularcommunication systems, now commonly locate the radios next to theantennas on the tower outside of the communications shelter.

In these next-generation facilities, the baseband system module thatcontrols radio traffic is still located at the ground level shelter, butthe radios are separated from the controllers up to several hundred feetand controlled by fiber optic links. The radios are powered directly byDC feeds from the DC power plant that extend up the tower and to theradios. In some cases, the DC cables and fiber optic cables are runseparately up the tower and in other cases they are all bundled togetherin one large hybrid cable.

Optical fiber signal testing often increases connection complexity andthe load of installed equipment, such as passive components and fiberpatchcords. Optical fiber testing also may increase connectivityfailures as correct polarity becomes difficult to control and challengesinfrastructure management in the already densely populated communicationsites. As a result, telecommunication vendors often avoid implementingmonitoring solutions downgrading the quality of the network physicallayer infrastructure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a communication system that uses a modular opticalinterface.

FIG. 2 shows a circuit diagram for the modular optical interface.

FIG. 3 shows a splitter holder used in the optical interface.

FIG. 4 shows a fiber optic module used in the optical interface.

FIG. 5 shows fiber optic modules horizontally inserted into a rackenclosure.

FIG. 6 shows an opposite view of the rack enclosure of FIG. 5.

FIG. 7 shows fiber optic modules vertically inserted into a multi-columnenclosure.

FIG. 8 shows an opposite view of the rack enclosure of FIG. 7.

FIGS. 9 and 10 show covers extending over ends of the enclosures shownin FIGS. 7 and 5, respectively.

DETAILED DESCRIPTION

Several preferred examples are described with reference to theaccompanying drawings. Various other examples are also possible andpractical. The suppression system may be exemplified in many differentforms and should not be construed as being limited to the examples setforth.

An optical interface includes a rack mountable enclosure that includesmultiple slots for retaining multiple insertable fiber optic (FO)modules. The FO modules include a first set of interconnection portsthat connect to remote radio units (RRUs), a second set ofinterconnection ports that connect to a baseband unit (BBU), and a thirdset of monitoring ports that connect to monitoring/text equipment. TheFO modules contain fiber splitters that split off uplink/receive anddownlink/transmit signals carried on optical fibers to the third set ofmonitoring ports. The FO modules may insert in different orientationsand directions into different rack mountable enclosure configurationsfor higher density and more configurable connectivity. A splitter holderis located within the FO module and provides improved optical fiberrouting for more integrated module port interconnectivity.

FIG. 1 illustrates one example distributed wireless communication system12. A building 24 contains computing equipment for a base transceivercommunication station (BTS) 46. BTS 46 may be contained in a rack 47. Afiber to the antenna (FTTA) architecture connects communication station46 through coaxial fiber optic (FO) cables 38 to different remote radiounits (RRUs) 18 located on the top of a tower 14.

The FTTA architecture reduces signal loss over FO cables 38 by movingradio frequency (RF) circuits from BTS 46 to RRUs 18 and closer to radiotransceiver antennas 16. The RRUs 18 communicate with a baseband unit(BBU) 48 in BTS 46 through bidirectional (Tx/Rx) low loss optical fiberlinks in FO cables 38 using a transmission protocol such as commonpublic radio interface, open base station architecture initiative.

In order to protect active equipment ports and enhance systemflexibility (reconfiguration & maintenance), FO cables 38 are notdirectly terminated on BBU 48 but terminated on an intermediate opticalinterface (OI) subrack 50 contained on rack 47. Common fiber patchcords52 then connect optical interface 50 to baseband unit 48.

In other examples, radios 18 may be located on the top of a buildingthat also houses DC power plant 44 and communication station 46. Inanother configuration, radios 18 and associated antennas 16 are locatedat different corners on the roof of a building.

A direct current (DC) power plant 44 is connected through a DC power bus42 and DC power cables 30 to the different radios 18 on tower 14. Aremote suppression unit 20 may be attached to a support 22 on top oftower 14 and connected to the remote ends of power cables 30 proximateto radios 18 and antennas 16.

A local rack based suppression unit 40 is located inside of building 24and connected to the opposite local ends of power cables 30 relativelyclose to DC power plant 44 and communication station 46. In oneembodiment, suppression unit 40 is located in a rack 26 that alsocontains DC power plant 44. In another example, suppression unit 40 islocated in another rack or some other location next to power plant 44.

Other suppression and optical fiber units are described in the followingpatents which are all incorporated by reference in their entireties:

Patent application Ser. No. 12/984,304 filed Jan. 4, 2011, entitled:OVERVOLTAGE PROTECTION SYSTEM FOR RADIO HEAD-BASED WIRELESSCOMMUNICATION SYSTEMS;

Patent application Ser. No. 13/005,275 filed Jan. 12, 2011; entitled:OVERVOLTAGE PROTECTION FOR REMOTE RADIO HEAD-BASED WIRELESSCOMMUNICATIONS SYSTEMS; and

Patent application Ser. No. 13/301,685 filed Nov. 21, 2011; entitled:MODULAR AND WEATHER RESISTANT OVERVOLTAGE PROTECTION SYSTEM FOR WIRELESSCOMMUNICATION SYSTEMS.

FIG. 2 depicts an example connection diagram for optical interface 50shown in FIG. 1. Optical interface 50 provides a more effective systemfor performing network maintenance and troubleshooting operations, suchas fiber physical integrity investigation, attenuation spatialresolution, etc. Optical interface 50 avoids the transmissioninterruptions and unwanted downtime typically associated with testingfiber links.

Coaxial fiber optic cables 38 in FIG. 1 may include multiple pairs ofuplink optical fibers 38A and downlink fibers 38B each connected to adifferent RRU 18. Fiber patchcords 52 in FIG. 1 also may includemultiple pairs of uplink fibers 52B and downlink fibers 52A connectingto BBU 48.

A first set of interconnection ports 58 connect uplink optical fiber 38Ato fiber splitter 54A via fiber 39A and connect downlink optical fiber38B to fiber splitter 54B via fiber 66A. A second set of interconnectionports 62 connect downlink fiber 52A to fiber splitter 54B via fiber 53Aand connect uplink optical fiber 52B to fiber splitter 54A via fiber64A. A third set of monitoring ports 68 connect to fiber splitter 54Avia fiber 64B and connect to fiber splitter 54B via fiber 66B.

Fiber splitters 54 enable network maintenance without breaking activelinks between RRUs 18 and BBU 48 thus eliminating downtime. For example,fiber splitter 54A includes passive optical components that splitoptical signals on uplink fiber 38A into separate duplicate opticalsignals on optical fibers 64A and 64B.

Uplink signals on optical fibers 64A and 64B are duplicate portions ofthe same common optical uplink signal received on uplink fiber 38A.Uplink signals on fiber 64A may connect via port 62B and uplink fiber52B to active communication equipment in BBU 48 while the same uplinksignals on fiber 64B may connect via monitoring port 68A tomonitoring/test equipment (not shown).

An operator may use the monitoring/test equipment connected tomonitoring ports 68 to perform testing operations, such as powermeasurements, out of band optical time domain reflectometry, or radiofrequency (RF) over common protocol radio interface measurements. Sincea separate uplink signal is connected via fiber 64B to monitoring port68A, the test equipment may perform tests without interrupting signaltransmissions between RRU 18 and BBU 48.

Power levels at each uplink signal 64A and 64B may depend on thespecific specifications for optical fiber splitter 54A. A splittingratio and number of output ports on fiber splitter 54A can vary from 1%to 99% of the input signal power on uplink fiber 38A. For example, fibersplitter 54A may split the power of uplink signals on fibers 64A and 64Beach by 50% of the signal power on uplink fiber 38A.

Efficient signal monitoring may require control on both transmitting(Tx) and receiving (Rx) directions. Therefore, second fiber splitter 54Bsplits downlink signals transmitted from BBU 48 to RRU 18 on downlinkfiber 52A into two downlink signals on fibers 66A and 66B. The splitdownlink signal on fiber 66A goes to RRU 18 via port 58B and fiber 38B.The split downlink signal on fiber 66B does to the monitoring/testequipment via monitoring port 68B. Fiber splitter 54B may divide outputpower levels similar to fiber splitter 54A. Fiber splitters 54 are knownto those skilled in the art and are therefore not described in furtherdetail.

FIG. 3 shows a splitter holder 80 that contains multiple fiber splitters54. Splitter holder 80 has an oval shape with substantially flatparallel upper and lower sections 82A and 82B, respectively, and roundends sections 86 extending between top and bottom sections 82A and 82B.Channel walls 84 extend radially out and around an outside surface ofsplitter holder 80 forming separate channels 88. A plate 90 retains thefirst and second set of interconnection ports 58 and 62, respectively,and a plate 92 retains the third set of monitoring ports 68.

The elongated oval shape of channels 88 provide compact routing ofoptical fibers to different ports. For example, a first optical uplinkfiber 39A extends from interconnection port 58A, over flat top section82A of splitter holder 80, and to a first end of upper fiber splitter54A. Uplink fiber 64A extends from a second end of upper fiber splitter54A, around round end section 86 and along bottom section 82B ofsplitter holder 80, and connects to one of the second set ofinterconnection uplink ports 62B. A third uplink fiber 64B extends fromthe second end of upper fiber splitter 54A, along top section 82A of thesplitter holder 80, and connects to one of uplink monitoring ports 68A.

The same channel 88 retains a set of optical downlink fibers includingfiber 53A extending from interconnection port 62A, along bottom section82B of splitter holder 80, and to a first end of lower fiber splitter54B (see FIG. 1) located underneath bottom section 82B. A seconddownlink fiber 66A extends from a second end of lower fiber splitter54B, around round end section 86 and along top section 82A of splitterholder 80, and connects to interconnection port 58B. Optical downlinkfiber 66B extends from the second end of lower fiber splitter 54B,underneath bottom section 82B of splitter holder 80 and connects tomonitoring port 68B.

Uplink fibers 38A and 39A include snap connectors 94 that snap into andinterconnect via interconnection ports 58A and downlink fibers 38B and66A include snap connectors 94 that snap into and interconnect viainterconnection port 58B. Uplink fibers 52B and 64A include snapconnectors 94 that snap into and interconnect via interconnection port62B and downlink fibers 52A and 53A include snap connectors 94 that snapinto and interconnect via interconnection port 62A. Uplink fiber 64B anddownlink fiber 66B include snap connectors 96 that snap into monitoringports 68A and 68B, respectively.

After fibers are run through a channel 88, individual caps 97 areattached over top section 82A and bottom section 82B of splitter holder80. Caps 97 insert into notches 98 formed in channel walls 84 of channel88 and are held down with screws 99.

Splitter holder 80 routes fibers to ports 58, 62, and 68 in a spaceefficient manner enabling fast, clean installation, and high terminationdensity. Channels 88 provide both physical and visual fiber separationfor efficient fiber management and provides minimum bending radiusrequirements eliminating signal attenuation and signal loss introducedby improper routing. Reducing signal losses support state of the artwavelength divisional multiplexing (WDM) architectures.

FIG. 4 shows a fiber optic module 100 that retains splitter holder 80.Splitter holder 80 sits inside of a container that includes a base plate102. Bottom ends of mounting plates 90 and 92 insert in between andattach via screws to side walls 104 that extend up along the sides ofbase plate 102. A container cover 105 extends over splitter holder 80,baseplate 102, and mounting plates 90 and 92. Walls 106 extend down fromsides of cover 104 and attach via screws to an upper end of mountingplates 90 and 92. Interconnection ports 58 and 62 extend in rows orcolumns out from a first end of module 100 and monitoring ports 68extend in a row or column out from of a second end of module 100.

FIG. 5 shows one example back view for an optical interface 50 that usesa rack enclosure 120 for retaining multiple FO modules 100. Enclosure120 includes substantially flat parallel first and second walls 122 and124, respectively, extending from a first end 128 to a second end 130.Side walls 126 extend between sides of first and second walls 122 and124 from first end 128 to second end 130. Dividers 132 extend betweenfirst wall 122 and second wall 124 from first end 128 to second end 130forming slots 134. Enclosure 120 may have a U1 dimensional profile thatcontains three slots 134.

Fiber optical modules 100 are configured to sliding insert horizontallyalong a lateral axis into slots 134. A first module 100A is shown fullyinserted into one of slots 134 and a second module 100B is shownpartially inserted into one of slots 134. Modules 100 are symmetric sothat either end can be inserted into slot 134. In one example, a firstend of module 100 retaining interconnection ports 58 and 62 is insertedinto slot 134 and extends out end 128 of enclosure 120. In anotherexample, a second end of module 100 retaining monitoring ports 68 isinserted into slot 134 and extends out end 128 of enclosure 120. Thedifferent insertion directions for modules 100 increase the types ofport configurations configurable in enclosure 120.

Ears 138 may attach enclosure 120 to BTS rack 47 that also may retainBBU 48 (see FIG. 1). Retaining arms 136 extend from side walls 126 onends 128 and 130 of enclosure 120. Retaining arms 136 support ends ofoptical fibers that connect to monitoring ports 68 and interconnectionports 58 and 62. The optical fibers may connect to the ports and thenrun laterally out through openings 135 formed in retaining arms 136. Acover 140 may extend over end 128, retaining arms 136, and the ends ofoptical fibers connected to the interconnection ports ports 58 and 62.Another similar cover 140 may extend over end 130, monitoring ports 68,and over the ends of optical fibers connected to monitoring ports 68.Covers 140 prevent technicians from accidentally bumping the opticalfibers and disrupting signal transmissions.

Enclosure 120 receives up to three pluggable/replaceable modules 100each containing a splitter holder 80 (FIG. 3). Each splitter holder 80is configured to accommodate up to 12 fiber splitters 54 supporting sixpairs of bidirectional uplink/downlink fibers for connecting to sixRRUs. This compact solution enables channel monitoring via monitoringports 68 without increasing the load of the installed components andwithout adding complexity since the network comes fullypreconnectorized.

FIG. 6 shows an opposite perspective front view of rack enclosure 120.In this example, modules 100 are configured to insert in from anopposite end of enclosure 120. Modules 100 may include angled brackets133 that press up against a front face of dividers 132. Screws 137insert through holes in brackets 133 and threadingly engage with holesformed in dividers 132. Retaining arms 136 attach to the sides ofmodules 100 opposite of brackets 133.

FIG. 7 shows a back view for another enclosure 150 with standard 3U 19inch rack dimensions or 3U-23 inch rack dimensions. Enclosure 150includes substantially flat parallel first and second walls 152 and 154,respectively, extending from a first end 158 to a second end 160. Sidewalls 156 extend between sides of first and second walls 152 and 154from first end 158 to second end 160.

Dividers 162 extend between first wall 152 and second wall 154 fromfirst end 158 to second end 160 forming slots 164. Modules 100 insertalong a vertical elongated lateral axis into slots 164 and can also beinserted into slots 164 from either end. The 3U 19 inch rack enclosure150 receives up to eight pluggable/replaceable modules 100 eachcontaining a splitter holder 80 (FIG. 3). The 3U 23 inch rack enclosurereceives up to ten pluggable/replaceable modules 100. Of course otherenclosure configurations can also be used.

Ears 168 may attach enclosure 150 to BTS rack 47 that also may retainBBU 48 (see FIG. 1). Retaining arms 166 extend from side walls 156 onfirst end 158 and second end 160. Retaining arms 166 support ends ofoptical fibers that connect to monitoring ports 68 that extend out fromend 160. Other retaining arms 166 extending from end 158 support endsfor a second set of fibers that connect to interconnection ports 58 and62 (not shown). A cover 170 may extend over end 158, retaining arms 166,and the ends of the optical fibers connected to the interconnectionports 58 and 62.

FIG. 8 shows an opposite perspective front view of rack enclosure 150.In this example, modules 100 are configured to insert in from anopposite end of enclosure 150. Modules 100 may include angled brackets165 that press up against a front face of dividers 162 (see FIG. 7).Screws 167 insert through holes in brackets 165 and threadingly engagewith holes formed in dividers 162 (see FIG. 7). In this example, pullplates 169 are attached to top ends of FO modules 100. Pull plates 169include L-shaped fingers that extend out from a front end of modules 100that a technician uses to insert and remove FO modules 100 from rack 150without disrupting the fiber lines connected to ports 58 and 62.

FIG. 9 shows another view of enclosure 150 with cover 170 attached overend 160 and monitoring ports 68. FIG. 10 shows another view of enclosure120 with cover 140 attached over end 130 and monitoring ports 68. Covers140 and 170 may comprise a transparent plastic so that technicians canview the connections between optical fibers and the interconnectionports and monitoring ports.

Optical interfaces 50 in FIGS. 5-10 offer a flexible and expandableinstallation scheme supporting up to 240 front patching-LCfootprint-terminations (or 60 RRUs) and the corresponding monitoringports. Despite the high maximum capacity, the design and layout of theoptical interface and the associated ports provide easy access tointerconnection points.

Multiple bracket mounting options allow FO modules 100 to be installedwith monitoring ports at the front or the rear end of the 1U or 3Uenclosure trays providing interchangeable installation alternatives tosupport site expandability and topology optimization.

Other advantages of the modular optical interface 50 includes compactdesign, a fully preconnectorized solution, multiple modular installationoptions, advanced expandability with easy maintenance and componentreplacement, high termination density, easy access to ports, easyconnector handling, minimum attenuation complying with strict WDMrequirements, stable dedicated channel routing for stable opticalperformance, and integrated cable management and protection for highdensity applications.

Only those parts of the various units are shown and described which arenecessary to convey an understanding of the examples to those skilled inthe art. Those parts and elements not shown may be conventional andknown in the art. Having described and illustrated the principles of theinvention in a preferred embodiment thereof, it should be apparent thatthe invention may be modified in arrangement and detail withoutdeparting from such principles.

We claim all modifications and variation coming within the spirit andscope of the following claims.

The invention claimed is:
 1. An optical fiber module, comprising: amodular container configured to slidingly insert into a slot formed inan enclosure; fiber splitters located within the module containerconfigured to split optical signals on optical fibers into separateduplicate optical signals; a first set of interconnection portsextending from the modular container for connecting the fiber splittersto remote radio units (RRUs); a second set of interconnection portsextending from the modular container for connecting the fiber splittersto a baseband unit (BBU); and a third set of monitoring ports extendingfrom the modular container for connecting the fiber splitters tomonitoring equipment, the first and the third interconnection portsreceiving from the fiber splitters the duplicate optical signalsreceived from the optical fibers connected to the second set ofinterconnection ports and the second and third interconnection portsreceiving from the fiber splitters the duplicate optical signalsreceived on the optical fibers connected to the first set ofinterconnection ports.
 2. The optical fiber module of claim 1 whereinthe modular container comprises a rectangular shape and inserts into aslot in a U1 or U3 enclosure.
 3. The optical fiber module of claim 1wherein the first and second set of interconnection ports extend from afirst end of the modular container and the third set of interconnectionports extend from a second opposite end of the modular container.
 4. Theoptical fiber module of claim 3 wherein: the first set ofinterconnection ports extend along a first laterally elongated axis ofthe modular container; the second set of interconnection ports extendalong in a second axis parallel with the first laterally elongated axis;and the third set of monitoring ports extend along in a third axisparallel with the first laterally elongated axis.
 5. The optical fibermodule of claim 1 wherein: the first set of interconnection portsinclude both uplink ports for connecting to optical fibers carryinguplink signals received from the RRUs and downlink ports for connectingto optical fibers carrying downlink signals transmitted to the RRUs; thesecond set of interconnection ports include both uplink ports forconnecting to optical fibers carrying the uplink signals to the BBU anddownlink ports for connecting to optical fibers carrying the downlinksignals received from the BBU; and the third set of interconnectionports include both uplink ports for connecting to optical fiberscarrying the uplink signals received from the RRUs and downlink portsfor connecting to optical fibers carrying the downlink signals receivedfrom the BBU.
 6. The optical fiber module of claim 1 wherein the modularcontainer includes: a base plate with side walls for retaining the fibersplitters; retaining plates attached to a first and a second end of thebase plate configured to retain the first, second, and third set ofports; and a cover configured to attach over the base plate, fibersplitters, and the retaining plates.
 7. The optical fiber module ofclaim 1 including a splitter holder located within the modular containerincluding multiple channels each retaining the fiber splitters andoptical fibers associated with a different one of the RRUs.
 8. Theoptical fiber module of claim 7 wherein some of the optical fibers wraparound rounded ends of the splitter holder.
 9. The optical fiber moduleof claim 7, wherein the splitter holder includes an oval shaped profilewith flat top and bottom sections and round ends sections extendingbetween the top and bottom sections.
 10. The optical fiber module ofclaim 9, including: a first set of optical uplink fibers extending fromthe first set of interconnection ports, over the flat top section of thesplitter holder, and to first ends of an upper set of the fibersplitters located on the flat top section of the splitter holder; asecond set of optical uplink fibers extending from second ends of theupper set of fiber splitters, around one of the round end sections andalong the bottom section of the splitter holder, and connecting to oneof the second set of interconnection ports; and a third set of opticaluplink fibers extending from the second ends of the upper set of fibersplitters, along the top section of the splitter holder and connectingto the third set of monitoring ports.
 11. The optical fiber module ofclaim 9, including: a first set of optical downlink fibers extendingfrom the second set of interconnection ports, along the bottom sectionof the splitter holder, and to first ends of a lower set of the fibersplitters located on the bottom section of the splitter holder; a secondset of optical downlink fibers extending from second ends of the lowerset of fiber splitters, around one of the round end sections and alongthe top section of the splitter holder, and connecting to one of thefirst set of interconnection ports; and a third set of optical uplinkfibers extending from the second ends of the lower set of fibersplitters, along the bottom section of the splitter holder andconnecting to the third set of monitoring ports.